The present disclosure is directed toward rotary actuators, and more particularly toward DC brushless motor control for rotary actuators.
DC motors for use in rotary actuators are typically brushless DC poly-phase motors. A standard DC motor includes a plurality of motor poles, each of which includes multiple commutation steps (steps within each pole). By way of example a brushless DC three-phase motor includes six motor poles, each of which has six commutation steps. This results in a total of thirty-six commutation steps around the shaft, with each of the commutation steps being approximately ten degrees offset from each adjacent commutation step. Motors of this type are typically controlled by a sensor capable of determining the rotary position of the shaft, and thereby determining the number of and approximate location of commutation steps needed in order to apply a desired rotation.
In a standard DC motor, it is assumed that the commutation steps are evenly distributed around the shaft. Known methods for determining how many commutation steps to rotate the shaft in order to achieve desired angle of rotation divide the desired angle of rotation by the assumed angular distance between commutation steps. The resulting integer is the number of commutation steps that the shaft is rotated. If variations are present in the angular distance between commutation steps, then the resulting rotation provides an incorrect location of commutation change, reducing available torque, efficiency, and peak velocity.